A SCOPING STUDY ON THE EPHEMEROPTERA OF SOUTHERN CHALK STREAMS A Report to the Envinulinent Agency .1 F Wright .1 II Blackburn 121 NI Gunn K I. Symes •1 Bowker Institute of htshuater Ecology River Laboratory East Stoke W.NI2E11.1N1 121120 611B A pril 1998 =I IM 61•1•11111•1=10110110111100 MEN Scoping Study on the Ephemeroptera of Southern Chalk Streams J F Wright, J H Blackburn, R J IVIGunn, K L Symes & J Bowker Research contractor: Institute of Freshwater Ecology Environment Agency Rivers House Sunrise Business Park Higher Shaftesbury Road Blandford Forum DTI 1 8ST Publishing Organisation Environment Agency Rivers House Sunrise Business Park Higher Shaftesbury Road Blandford Forum DT11 8ST Tel 01258 456080 Fax: 01258 455998 C) Environment Agency 1998 All rights reserved. No part of this document may be produced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without the prior permission of the Environment Agency. The views expressed in this document are not necessarily those of the Environment Agency. Its officers servant or agents accept no liability whatsoever for any loss or damage arising from the interpretation or use of the information, or reliance upon views contained herein. Dissemination Status Internal: Released to South-West, Southern, Thames and Anglian Region. External: Restricted Statement of Use This short scientific review was commissioned to further a 'LEAP' action to investigate factors which potentially could contribute to an alleged decline in Ephemeroptera within the Avon catchment. The review has relevance to other chalk systems within the UK and should significantly contribute to the Agency's knowledge, enabling future monitoring to be focused on specific aspects which influence this group. Research Contractor This document was produced under the Technical Services Agreement by: Institute of Freshwater Ecology River Laboratory East Stoke Wareham Dorset BH20 6BB Tel: 01929 462314 Fax. 01929 462180 Environment Agency Project Manager Mr A. Frake, Environment Agency, South West Region. ACKNOWLEDGEMENTS The authors would like to thank the Environment Agency, South West Region for initiating this study. In particular, we thank Dr. G.P.Green and Dr. D.A.Cooling for helpful discussions at the outset and Mr. A Frake for his advice as Nominated Officer to the project. Funding for the report was provided under the Technical Services Agreement between the Environment Agency and the Institute of Freshwater Ecology. INTELLECTUAL PROPERTY RIGHTS CONFIDENTIALITY STATEMENT 'In accordance with our normal practice, this report is for the use only of the party to whom it is addressed, and no responsibility is accepted to any third party for the whole or any part of its contentg Neither the whole nor any part of this report or any reference thereto may be included in any published document, circular or statement, nor published or referred to in any way without our written approval of the form and context in which it may appear.' WIIMMIIINIMUNIIMMIIMMIMMININIMOINIII0 CONTENTS Page Acknowledgmen ts List of Tables List of Figures List of Appendices Executive Summary vii Key Words viii I. Introduction 1.1 Background to the Study 1 1.2 The British Ephemeroptera (mayflies) 1 2. The Ephemeroptera of southern chalk streams 3 2.1 Species characteristic of southern chalk streams 3 2.2 Seasonal occurrence of larvae 5 2.3 Species richness at chalk stream sites 6 2.4 Longitudinal occurrence of species 8 2.5 Abundance of families at chalk stream sites 9 3. Notes on the life cycles of each species 13 4. Factors affecting the distribution and abundance of Ephemeroptera 17 4.1 Habitats, habits and feeding behaviour of the larvae 17 4.2 The impact of discharge regime 19 4.3 The impact of pollution 21 4.4 Factors affecting the terrestrial (adult) phase 23 5. References 25 Appendices 29 1•11-1•11•11MOIIININIIIIIIIMIN•11•1111•10 a IIMINI LIST OF TABLES Page 21 Listing of the mayflies recorded at 42 chalk stream sites, together with 4 I the numbcr of sites at which each taxon was found. Data from RIVPACS samples (three seasons samples combined) I 2.2 Frequency of occurrence of mayfly larvae in 42 chalk stream sites 6 by season I 2.3 Longitudinal occurrence of mayfly larvae at 42 chalk stream sites 9 3.1 Information on the flight periods and life cycles of mayflies abstracted 14 I from Elliott & Humpesch (1983) and Elliott eta (1988), together with additional observations made on southcrn chalk streams 1 4 1 Running-water habitats (from Wright et al. 1993), together with 17 habits and feeding behaviour (from Elliott c/at 1988) for the I mayflies found in southern chalk streams I LIST OF FIGURES 2 I Number of species of mayfly larvae recorded at 42 chalk stream sites 7 22 Mayfly species richness for 42 chalk stream sites in relation to location 7 downstream 2.3 Log. category abundance data for each mayfly family at 42 chalk stream I 1 sites in spring, summer and autumn. LIST OF APPENDICES I Appendix 1. Specification for the scoping study 29 Appendix 2. The 42 southern chalk stream sites for which RIVPACS samples 30 I have been obtained. Appendix 3. Mayflies found at each of the 42 chalk stream sites Data for the 31 1 three seasons are combined (1 indicates taxon occurrence in a single season, whereas 2 (or 3) indicates presence in two (or 3) seasons. I 1 MINIMIINIIIMMINIIIIIMMINIIIIIIMISM EXECUTIVE SUMMARY This scoping study was undertaken at the request of the Environment Agency, following expressions of concern from fishermen that some species of Ephemeroptera (mayflies) appear to have declined on the R.Wylye and on the upper reaches of the Hampshire Avon. The purpose of this scoping study is to provide a short scientific review of the mayfly fauna of southern chalk streams. • Forty nine species of mayflies are known to occur in Britain. The status of two additional species is uncertain. An appraisal of the R1VPACS III data-base yielded 42 high quality sites on southern chalk streams. Examination of the species lists for these sites confirmed that over 50% of the British species occur on southern chalk streams. Information is provided on the seasonal occurrence of the different species and their frequency of occurrence at the 42 sites. Between four and fifteen species of mayflies were recorded per site, with an arithmetic mean of 9.12 per site. The most species-rich sites (12 or more species) occurred between 10 and 50, km from stream source. They included sites on such well known rivers as the R. Frome (Dorset), R. lichen, R. Lambourn, Moors River (Dorset) and R.Test. The study includes information on the longitudinal occurrence of each species. The R1VPACS III data-set also includes information on the log, categories of abundance of each family of mayfly in spring, summer and autumn, based on the standard R1VPACS pond-net samples. This provides a useful general guide on whether a given family is scarcc, common or abundant in a given season. Members of the Baetidae were found to be important components of the mayfly fauna in spring, summer and autumn, but were particularly abundant at most sites in summer. Ephemerellidae were also very abundant at most sites in summer. Notes are provided on the flight period and life cycles of each species, as far as these are known The life cycles of some species show flexibility and some members of the Baetidae are capable of having several generations in a year. Hence, interpretation of the life cycle can pose problems Information on the habitats, habits and feeding behaviour of the larvae demonstrates that a wide variety of different habitats and food resources are exploited by mayfly larvae. A consideration of the potential impact of flow regime on larval populations suggests that if changes in the flow regime affect the habitats and food resources within a stream, then there are likely to be consequences for the mayfly fauna. However, different members of the mayfly fauna may respond in different ways, given their various adaptations. Low flows arc of particular interest at present, and several short term studies on chalk streams, together with one long-term study on the R.Lambourn in the 1970's, are starting to provide scientific data on the way in which different components of the VII mayfly fauna appear to respond to the discharge regime. Some provisional findings for the Baetidae, Ephemerellidae and Ephemeridae are given below. A nine-year study on the R. Lambourn provided evidence that in early June, densities of larvae in the Baetidae (which may have included up to six species) were low in drought years (-500 ni2) compared with some years with high discharge when densities were —5,000 1112. Densities of larvae in the Ephemerellidae (Ephemerella ignita only) were higher in the year following a drought. Densities of larvae in the Ephemeridae (Ephemera danica only) did not appear to be related to the prevailing discharge regime in the R. Lambourn. Instead, cool damp conditions during the period of flight activity in May/June of one year resulted in very low larval densities of the next generation in December of that year. Over the next three generations (at intervals of two years), larval densities increased progressively in the December following oviposition. Studies commissioned by the Environment Agency on a number of chalk stream sites first examined in the 1970's may soon provide further information on the response of mayflies to the flow regime. Some chalk streams may be subject to organic pollution as a result of sewage effluent, fish farm effluent or farm wastes. Low levels of organic enrichment may not have adverse effects on the mayfly fauna, but more severe cases of organic pollution will result in the progressive elimination of the more sensitive species.